Make PrimitiveNode work with a variable amount of inputs.
Added more general "primitives" with Initial Value Transformers (see https://docs.google.com/document/d/1MHnDg1OsFy-SWD_30z7zrTRAik0Qhdbp70TYdOZd-r0/edit?usp=sharing)
Also added the Native node state, defining state as a separate value. This is in preparation of changing the return type of (Event a -> b -> Event b) and not needing the "old" value (b) in those functions anymore.
Removed old in favour of special Native.Signal.NoUpdate' value. Fixed delay and timestamp implementations.